// Author: combacsa@kaist.ac.kr
// http://www.jungol.co.kr/prog/Hanal/hanalView.php?qs_code=132

//#define COMPILE
#ifdef COMPILE

#include <fstream>
using namespace std;

int main() {
	ifstream in("input.txt");
	int n;
	in >> n;
	in.close();
	int sum = 0;
	for (int i = 1; i <= n; i++) {
		if ( i % 5 == 0) {
			sum += i;
		}
	}
	ofstream out("output.txt");
	out << sum << endl;
	out.close();

	return 0;
}
#endif
